1. Field of the Invention
The present invention relates to lenses used in optical systems and, more particularly to a new lens or a new lens group.
2. Description of the Prior Art
Introducing the desired amount of distortion in an optical system is possible and relatively straight forward for optical designers. Known fxcex8 lenses (as in U.S. Pat. Nos. 4,695,132 issued on Sep. 22, 1987 to Sakuma and No. 4,770,517 issued on Sep. 13, 1998 also to Sakuma) used in laser scanner systems are one of the most popular lenses of this type. Over the past decade or two, system improvements have shifted product emphasis toward electronic features and digital processing, such that optical system design has frequently been relegated to a low priority. Recently, there has been a revival of interest in solving optical problems with innovative optical design. On the other hand, it is possible to simplify considerably the task of the software by designing more sophisticated optical elements.
For example, a spectrometer uses a diffraction grating to spread the spectral component of a light incident of the grating on a one (1) dimensional detector. However, on the detector, the spectral components are not spread linearly such that the resolution is thus not constant and the calibration process must be applied very carefully to prevent error.
It would thus be desirable to have a lens, or group of lens, which when used with a diffraction grating would yield a linear output thereby substantially eliminating a time consuming calibration process.
It is therefore an aim of the present invention to provide a new lens or lens group.
It is a also an aim of the present invention to provide a new system which combines the new lens and a diffraction grating providing a linear output plane as a function of the wavelength (xcex), or of the order of diffraction (m), or of the grating spatial frequency (1/xcex9), or of the inverse of the index of refraction (n).
It is a further aim of the present invention to provide a new lens or lens group with proper amount of distortion to provide a f-Sin(xcex8) characteristic. The optical lens may have a positive or a negative power and it can be refractive, diffractive and reflective or in combination.
Therefore, in accordance with the present invention, there is provided an optical system for obtaining a linear output from an incident light, comprising a diffraction grating and a lens having a f-Sin(xcex8) characteristic, where f is the effective focal length of said lens and xcex8 is an output angle of the light exiting from said diffraction grating, wherein a light incident on said diffraction grating reaches said lens and results in a linear output.
Also in accordance with the present invention there is provided an optical system for obtaining a linear output from an incident light, comprising a diffraction grating and a group of lenses having a f-Sin(xcex8) characteristic, where f is the effective focal length of said group of lenses and xcex8 is an output angle of the light exiting from said diffraction grating, wherein a light incident on said diffraction grating reaches said group of lenses and results in a linear output.
If a f-Sin(xcex8) lens or lens group is introduced for instance in a spectrometer, this new lens provides a correction for the deflection of the laser beam which takes place at a linear position with the wavelength in the detector plane. Specifically, when the diffraction grating is positioned on the entrance pupil of the f-Sin(xcex8) lens having an effective focal length of f, with respect to the optical axis thereof, the beam will be focussed onto the detector plane at a point which is displaced by a distance of f-Sin(xcex8) from the optical axis. According with the grating equation at normal incidence             Sin      ⁡              (        θ        )              =                  m        ·        λ                    n        ·        Λ              ,
where xcex8 is the diffraction angle, m is the diffraction order, xcex is the wavelength, n the index of the refraction and xcex9 the grating period, the distance from the optical axis of the focused beam is a linear function of the wavelength. Then the calibration can be simplified because the spectral component of a light signal spread on the detector is linearly distributed on the linear detector. Furthermore the resolution is constant over the wavelength operating range. The designation ,xe2x80x9cf-Sin(xcex8) lensxe2x80x9d, or xe2x80x9cf-xcex lensxe2x80x9d, is derived from such fact.
The present invention can solve the problem associated with the nonlinear imaging process in the spectrometer and it can solve also other problems. This invention is intended to provide a new lens or lens group which can be used with a diffraction grating to provide a linear output plane with the wavelength (xcex), but also with the order of diffraction (m), or with the grating spatial frequency (1/xcex9), or with the inverse of the index of refraction (n).
Accordingly, the invention provides a new lens or a new lens group with proper amount of distortion to provide a f-Sin(xcex8) characteristic. The optical lens or lens group of the present invention has a positive or a negative power and it can be refractive, diffractive and reflective or a combination of all these properties.